1. Field of the Invention
One embodiment of the present invention relates to a manufacturing method of graphene oxide. Another embodiment of the present invention relates to a secondary battery including graphene oxide and a manufacturing method thereof. Another embodiment of the present invention relates to a semiconductor device including a secondary battery.
Note that in this specification, a semiconductor device refers to any device that can function by utilizing semiconductor characteristics. An electro-optical device, a semiconductor circuit, and an electronic device are all semiconductor devices.
2. Description of the Related Art
With the downsizing of semiconductor devices, materials with high electrical conductivity and thermal conductivity have been required. Examples of the materials include graphene and graphene oxide. Recent research has been actively conducted on the use of carbon-based materials such as graphene and graphene oxide for components of batteries (lithium-ion secondary batteries and capacitors).
Graphene is a material having high strength, electrical conductivity, thermal conductivity, and heat resistance. Graphene is a single atomic layer consisting of six-membered carbon rings. Graphite is stacked layers of graphene.
Graphene oxide is obtained by Hummers' method (graphite is oxidized through the addition of concentrated sulfuric acid, sodium nitrate, and potassium permanganate), or modified Hummers' method (through the addition of KMnO4 to a mixture of concentrated sulfuric acid, phosphoric acid, and graphite). Commercially available graphene oxide, which is fabricated not by Hummers' method producing toxic gases but by modified Hummers' method or the like, is highly expensive.
Patent Document 1 discloses a method to obtain expansion graphite.